Geotechnical and micro-structural behaviour of chemically stabilized tropical residual soil

Abstract

The stabilization of soils with additives is a chemically modified method that can be used to improve soils with weak engineering properties. Non-traditional additives such as ionic, enzymes, salts, polymers, and tree resins are widely used for treating problematic soils. The effects of non-traditional additives on the geotechnical properties of soils have been the issue of investigation in recent years. The publications on macro-structural, micro-structural, and molecular characteristics of tropical residual soil stabilized by non-traditional stabilizers are limited. This research aimed at determining the stabilization mechanism and performance of the tropical residual (laterite) soil mixed with two types of non-traditional stabilizer; namely the calcium based powder stabilizer (SH-85) and sodium silicate based liquid stabilizer (TX-85). Macro-structural study including the compaction, unconfined compression strength, direct shear, and consolidation tests were used to assess the engineering properties of the stabilized soil. The physico-chemical bonding mechanisms contributed to the stabilization process were discussed based on the results of micro-structural study from different spectroscopic and microscopic techniques such as X-ray Diffractometry, Energy-Dispersive X-ray Spectrometry, Field Emission Scanning Electron Microscopy, Fourier Transform Infrared Spectroscopy, Surface Area Analysis and Thermal Gravimetric Analysis. In addition, the performance of treated laterite backfill stabilized with the selected additives was evaluated using series of physical model tests. The model tests consisted of strip footing placed on stabilized backfill behind sheet pile wall. The numerical simulation using PLAXIS finite element (FE) software was carried out to compare and evaluate the results obtained from the physical models. The laboratory tests showed that the addition of 9 % (as the optimum amount) of both additives increased more than 80% of compressive strength after 7 days of curing periods while the consolidation settlement had been effectively reduced. The micro-structural study revealed that the stabilization process modified the porous network of laterite soil. The pores of the soil had been filled by the newly formed compounds known as calcium aluminate hydrate cementitious material for SH-85 treated samples and sodium aluminosilicate hydrate gel-like product for TX-85 treated samples. Hence, the stabilization mechanism of two selected non-traditional additives was by cationic exchange and physical bonding. The numerical simulation and physical modelling showed identical trends. Therefore the finite element method using elasto-plastic Mohr-Coulomb model is suitable to be used in evaluating and predicting the behaviour of chemically stabilized backfill. The results from the physical model tests showed that the ultimate capacity of the footing placed on the stabilized backfill soil increased greatly while the settlement reduced compared to untreated backfill laterite soil, after just 7 days of curing. It can be concluded that the quick reaction of the selected stabilizers with laterite soils is very advantageous and cost-effective for geotechnical engineering projects.